# Dirichlet's Box Principle/Also known as

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## Dirichlet's Box Principle: Also known as

**Dirichlet's Box Principle**, in particular its corollary, is also commonly known as the **pigeonhole principle** or **pigeon-hole principle:**

- Suppose you have $n + 1$ pigeons, but have only $n$ holes for them to stay in.

- By the
**pigeonhole principle**, at least one of the holes houses $2$ pigeons.

It is also known as **(Dirichlet's) drawer (or shelf) principle**.

Some sources give it as the **letterbox principle** or **letter-box principle**.

## Sources

- 1989: Ephraim J. Borowski and Jonathan M. Borwein:
*Dictionary of Mathematics*... (previous) ... (next):**letter-box principle** - 1998: David Nelson:
*The Penguin Dictionary of Mathematics*(2nd ed.) ... (previous) ... (next):**Dirichlet's principle** - 2008: David Nelson:
*The Penguin Dictionary of Mathematics*(4th ed.) ... (previous) ... (next):**Dirichlet's principle**